Device for stamping by magnetic forming and associated method

ABSTRACT

A device for stamping a blank in order to produce a stamped part. The device includes a punch including a bearing surface, an anvil, and magnetic field generator. The stamping device has an initial position where the bearing surface of the punch receives a portion of a first surface of the blank, the anvil and the magnetic field generator are arranged on either side of another portion of the blank, with the anvil facing the first surface, and the magnetic field generator facing a second surface opposite the first surface. The magnetic field generator applies a pressure on the blank in a direction towards the anvil. The stamping device is also configured to move the punch relative to the magnetic field generator in a direction away from the anvil.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/EP2018/051134, having an International Filing Date of 17 Jan. 2018,which designated the United States of America, and which InternationalApplication was published under PCT Article 21(2) as WO Publication No.2018/134271 A1, which claims priority from and the benefit of FrenchPatent Application No. 1750370, filed on 18 Jan. 2017, the disclosuresof which are incorporated herein by reference in their entireties.

BACKGROUND 1. Field

This present disclosure relates to the field of forming, moreparticularly to stamping.

This present disclosure relates to a device and a method for stampingblanks by magnetic pulse for the production of stamped parts, inparticular parts referred to as deep drawn.

2. Brief Description of Related Developments

In the field of forming, in particular metals, stamping is a method thatis very often chosen, because it is robust and controlled well.

Stamping is commonly used in industry, in particular in the automobileindustry for forming in particular lining panels, such as a bonnet or adoor of a motor vehicle, due to the high production speeds that arepossible.

Stamping is a process for forming consisting in obtaining via theplastic deformation of a blank, under the action of a pressure, a partwith a more or less complex shape.

The device for stamping for implementing this method is comprisedsubstantially of a die and of a punch of practically complementaryshape, between which the blank is positioned. The obtained of the shapeis done by the driving of the blank under the action of the punch in thedie. The movement of the blank is generally controlled by ablank-holder, which imposes on it a retaining pressure, with the purposeof decreasing the appearance of folds or of tears on the final stampedpart.

However, in the presence of a part that is difficult to form, inparticular a deep-drawn part, the choice of the clamping force to beimprinted on the blank-holder is difficult. If the force of theblank-holder is too high, the folds are suppressed but the risk of atear is high. If the force of the blank-holder is too weak, the risk ofthe formation of folds is high.

In order to produce deep-drawn parts, alternatives to the method forstamping are known.

Among them, mention can be made of the hydro forming method. In thismethod, the blanks are formed by the action of a pressurised fluid.

The associated device for hydro forming is comprised ofhermetically-sealed chamber formed of two pieces of which one is ahollow mould that has an imprint complementary with the shape of thepart that is sought to be obtained. The blank is placed inside thechamber. A hydraulic pressure is exerted on the latter that thrusts itagainst the imprint of the mould. The fluid can be pressurised invarious ways. Among the existing methods of hydro forming, mention canbe made of the electro hydraulic forming method (EHF).

Such a method has many advantages, in particular a substantial reductionin the elastic return, or lower manufacturing costs. However, the majordisadvantages reside in the cycle time required for the stamping of thepart (water management time) and in the need to place the part to beformed in contact with water (corrosion possible).

Mention can also be made of the hot methods of forming, such as themethod for superplastic forming, referred to as SPF. This method isbased on the capacity of certain alloys, for example titanium, towithstand substantial deformation. These alloys, called in what followssuperplastic alloys, can reach elongations that sometimes range beyond1000% under certain conditions of temperature, pressure and deformationwhile conventional alloys are deformed generally only by about 20%.

The associated device for SPF forming is comprised of ahermitically-sealed chamber formed of two pieces of which one is ahollow mould that has an imprint complementary to the final externalgeometry of the part that is sought to be obtained. The blank is placedinside the chamber and fixedly maintained between the two pieces. Apressurised gas is injected into the chamber and thrusts the blank, bydeforming it, against the imprint. The pressure and the temperature, ofabout 900° C. for titanium alloys, must be perfectly controlled.

The obvious disadvantages linked to this device for forming SPF and tothe associated method reside in the cycle time, the cost and the factthat only certain materials can be used.

SUMMARY

This present disclosure has in particular for objective to overcome allor a portion of the limitations of the solutions of prior art, inparticular those mentioned hereinabove, by proposing a solution thatallows for the obtaining of stamped parts, and in particular ofdeep-drawn parts.

To this effect, the present disclosure aims firstly a device forstamping a blank in order to produce a stamped part comprising:

-   -   a punch comprising a bearing surface,    -   an anvil,    -   means for generating a magnetic field.

The term blank means a thin plate, in particular made of metal material.A plate is said to be thin when one of its dimensions is clearly lessthan the other two, typically at least one magnitude.

In an initial position, i.e. before the stamping phase, the device forstamping is configured in such a way that:

a. the bearing surface of the punch is intended for receiving a portionof a first surface of the blank,b. the anvil and the means for generating a magnetic field are intendedfor being arranged on either side of another portion of the blank.

The anvil is facing the first surface, and the means for generating amagnetic field are facing a second surface, opposite the first surface.The means for generating a magnetic field are distant from said secondsurface.

The means for generating a magnetic field are intended and configured toimprint on the blank a pressure in the direction of the anvil, in adirection ZZ′. This pressure projects the blank, in particular theportion of the blank with respect to the anvil, against the anvil. Thus,the pressure exerted partially thrusts in part the blank against theanvil, causing a deformation of said blank.

The device for stamping further comprises movement means arranged tomove the punch, relative to the means for generating a magnetic field,in a direction Z′Z, opposite the direction ZZ′. The punch isadvantageously moved in translation.

The punch and the anvil are preferably made from a metallic material inorder to contain the high pressures generated by the means forgenerating a magnetic field.

According to the present disclosure, the blank is intended to conform tothe shape of the punch in order to form the final stamped part.

The device for stamping according to the present disclosure isdifferentiated from the conventional devices for stamping in that thestamping is not carried out by the punch itself, but by the means forgenerating a magnetic field.

Likewise, the means for generating a magnetic field are used differentlyin the conventional framework of a magnetic forming method that formsthe whole of the blank at a single time. The means for generating amagnetic field are arranged in such a way as to not generate magneticpulses only on a portion of the blank. The relative displacement intranslation of the punch in relation to the means for generating make itpossible to move the zone of the blank that will be touched by themagnetic pulses.

Such a device advantageously makes it possible to work primarily incompression but also in expansion.

Such a device for stamping is thus particularly suitable for theproduction of stamped parts, in particular deep-drawn parts, withoutgenerating folds or tears in the part.

It is also suitable for the production of turned out edges, with theadvantages that can be provided by magnetic forming, such as theobtaining of radii of curvature less than 2 mm, fine edging, or of closetolerances, as well as the avoiding of cracking of the material in thezones with high elongation, in particular for aluminium.

According to preferred aspects, the present disclosure further respondsto the following characteristics, implemented individually or in each oftheir technically operative combinations.

According to preferred aspects of the present disclosure, the movementmeans comprise a linear actuator.

According to preferred aspects of the present disclosure, the means forgenerating a magnetic field comprises at least one coil.

According to preferred aspects of the present disclosure, the device forstamping comprises adjusting means configured to adjust the spacebetween the anvil and the means for generating a magnetic field.

According to preferred aspects of the present disclosure, the device forstamping comprises a blank-holder configured to impose a retainingpressure on the movement of the blank, against the punch.

The present disclosure also relates to a method for stamping by magneticpulse a blank in order to produce a stamped part, using a device forstamping in accordance with one of its embodiments. The method comprisesthe steps of:

a) positioning the blank in the device for stamping,

b) subjecting the blank to a magnetic field caused by the means forgenerating a magnetic field in such a way that a pressure is exerted onthe second surface of the blank in a direction ZZ′ and thrusts saidblank against the anvil,

c) moving the punch by the movement means in a direction Z′Z, oppositethe direction ZZ′, with the steps b) and c) being repeated, preferablysynchronised, until the desired shape is obtained for the finishedstamped part.

The term synchronised means that the steps are carried out eithersuccessively, one after the other, or simultaneously.

The blank is positioned in the device for stamping in such a way thatthe blank rests solely on the bearing surface of the punch.

As the punch moves, a magnetic pulse is generated by the means forgenerating, exerting, on the one hand, an axial pressure on the blank inthe direction of the anvil, thrusting said blank on said anvil, and onthe other hand, a radial pressure on the blank in the direction of thepunch, thrusting said blank on said punch.

The axial pressure projects a portion of the blank against the anvil.The radial pressure projects another portion of the blank against thepunch.

This double pressure, axial and radial, advantageously allows for boththe deformation of the blank and thrusting of it against the punch,making it match the shape of the latter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure shall be better understood when reading thedescription hereinafter, given as an example that is in no way limiting,and given in reference to the figures which show:

FIGS. 1 to 4 illustrate schematic cross-section views of an aspect of adevice for stamping according to the present disclosure showing thesuccessive steps of stamping of a blank,

FIG. 5 is a schematic view equivalent to FIG. 1 showing a particularembodiment of the device for stamping with a blank-holder.

In these figures, identical references from one figure to anotherdesignate identical or similar elements. For reasons of clarity, theelements shown are not shown to scale, unless mentioned otherwise.

DETAILED DESCRIPTION

A device for stamping 10, such as shown in FIGS. 1 to 4, is intended forthe stamping of blanks 50, for the purpose of producing stamped parts,in particular deep-drawn parts.

In an aspects of the present disclosure, the blanks 50 are made of ametallic material, such as steel.

The blank 50 has a first surface 51 and a second surface 52, oppositethe first.

In a preferred non-limiting aspect of the present disclosure, the devicefor stamping 10, such as shown as a cross-section in FIGS. 1 to 4, isadapted to the production of cups. The term cup means a stamped parthaving a hollow cylindrical shape.

Those skilled in the art will easily understand that the teaching ofthis present disclosure can be transposed to other aspects.

In this description, the terms such as upper, lower, top, bottom, left,right are used with a concern for simplicity, in reference to theorientation of the various elements shown in FIGS. 1 to 4. However,unless mentioned otherwise, these terms characterise only the relativearrangement of these elements, after a possible imaginary rotation inrelation to the effective orientation of the whole in space.

The device for stamping 10 comprises a first frame 20 and a second frame30. The first frame 20 can represent an upper portion of the device forstamping and the second frame 30, a lower portion, such as shown infigures. As an alternative, and without leaving the scope of the presentdisclosure, the first frame 20 can represent a lower portion, left orright, of the device for stamping and the second frame 30, respectivelyan upper portion, right or left.

First Frame

The first frame 20 carries a punch 21, preferably central.

Said punch comprises a bearing surface 211 and lateral walls 212.

In the particular example wherein the final stamped part is a cup, thepunch has the form of a cylindrical body, preferably full.

According to the present disclosure, the blank 50 is intended to conformto the shape of an outer surface of the punch 21.

Thus, the punch 21 has, on said outer surface, an imprint thatcorresponds to the shape of the final part, once stamped.

The punch 21 is mobile in translation, according to a vertical axis,thanks to movement means 23 that can move the punch between a retractedposition and a deployed position.

In the example of FIG. 4, the punch 21 is shown in deployed position.

The movement means 23 are actuated manually or automatically.

In an aspect of the present disclosure, the movement means 23 compriseat least one linear, hydraulic or pneumatic, actuator, such as acylinder operating between the first frame 20 and the punch 21. In thisembodiment, preferably, the fixed portion of the linear actuator—forexample the body of the cylinder—is housed in a recess (not shown) madein the first frame 20. The mobile portion of the linear actuator, forexample the piston of the cylinder, is able to be moved out of therecess in order to deploy the punch 21 and able to be moved to therecess in order to return the punch 21 to its initial position.Particularly advantageously, the movement of the punch 21 is controlledby control means.

In an alternative aspect of the present disclosure, the movement means23 have the form of a support carrying a pressure screw able tocooperate with the punch 21 in order to move it in translation.

The first frame 20 further comprises an anvil 22.

Said anvil is arranged around lateral walls 212 of the punch 21, whensaid punch is in its retracted position.

The anvil and the punch are spaced apart from one another by apredetermined distance.

In an aspect of the present disclosure, when the punch 21 has the formof a cylindrical body, the anvil 22 has the form of an annular bodysurrounding the punch.

In an aspect of the present disclosure, the anvil 22 can form the firstframe 20.

The punch, on its bearing surface, and the anvil, on a free end 221, areat separate heights.

Second Frame

The second frame 30 comprises a hollow body that delimits an open cavity33.

As shown in FIGS. 1 to 4, the hollow body is formed from an upperportion 31 and of lateral sides 32.

The second frame 30 is arranged with respect to the first frame 20 insuch a way that:

-   -   the open cavity 33 of the hollow body is intended to receive the        punch 21, when the latter is moved vertically, in a direction        Z′Z, to its deployed position,    -   the free ends 321 of the lateral sides 32 of the hollow body are        substantially facing the anvil 22.

The free ends 321 of the lateral sides 32 of the hollow body of thesecond frame are substantially facing the free end of the anvil 22.

The hollow body and the punch 21 have dimensions such that the punch 21can be moved freely in the open cavity 33 with, between their respectivesurfaces, a non-negligible space for the passing of the blank 50, in itsthickness.

In a non-limited aspect of the present disclosure, when the punch 21 hasthe form of a cylindrical body, the open cavity 33 has the form of anannular body surrounding the punch.

In an aspect of the present disclosure, the outer surface of the punch21 and the inner wall of the hollow cavity 33 are of practically thesame shape, to the nearest thickness of the final stamped part and anoperating clearance.

The second frame 30 further comprises means for generating a magneticfield 34.

The means for generating a magnetic field 34 are arranged, on free ends321 of the lateral sides 32 of the hollow body, facing the anvil 22.

As shown in FIGS. 1 to 4, the elements that form the device forstamping, namely the punch, the anvil and the means for generating amagnetic field 34 are arranged with respect to one another in such a waythat:

-   -   in an initial position of the device for stamping (FIG. 1), i.e.        before the beginning of the method for stamping, the blank 50 is        positioned flat between the various elements,    -   in a final position of the device for stamping (FIG. 4), i.e. at        the end of the method for stamping, the blank 50 is thrust        around the punch 21, forming the stamped part.

More precisely, regarding the initial position of the device forstamping shown in FIG. 1, the punch 21 is positioned in such a way thatits bearing surface 211, in a retracted or intermediate position, isintended to receive a central portion of the first surface 51 of theblank 50. The blank 50 rests on the bearing surface of the punch. Theanvil is positioned facing the first surface 51 of the blank 50, on aperipheral part of said blank and the means for generating a magneticfield 34 are positioned facing the second surface 52 of the blank, alsoon the peripheral portion of said blank. The first surface 51 of theblank is arranged at a distance from the free end 221 of the anvil 22.

The means for generating a magnetic field 34 are configured for andintended to create a magnetic field concentrated in a delimited spaceand over a very short period.

Preferably, such as shown in FIGS. 1 to 4, the means for generating amagnetic field 34, such as positioned, are thus able and intended toimprint on the blank 50 a pressure in the direction of the anvil 22, ina direction ZZ′. The pressure exerted partially thrusts the blankagainst the anvil 22, causing a deformation of said blank.

In an aspect of the present disclosure, the means for generating amagnetic field 34 are a coil.

The means for generating a magnetic field are more preferably anintegral part of a set that further comprises an electrical energystorage unit and one or several switches (not shown).

The electrical energy storage unit is configured for and intended tostore a moderate energy, for example of about a few kilojoules to a fewtens of kilojoules (kJ).

In a preferred aspect of the present disclosure, the storage unit is adischarge capacitor battery.

The first frame 20, the second frame 30, the anvil 22 and the punch 21are preferably made from a metallic metal, for example steel, so as tohave a structural resistance that makes it possible to contain the highpressures generated by the impact of the blank 50 on the anvil 22,during the method for stamping which shall be described hereinafter.

In an aspect of the present disclosure, the device for stamping 10comprises adjusting means (not shown) arranged to move the anvil 22vertically, in translation. Such means make it possible to reduce or toincrease the space e that separates the anvil from the means forgenerating a magnetic field 34. The sizing of the space e is accordingin particular to the material and the geometric shape of the punch, aswell as the pulse of the current. The sizing of the space e is maximisedin order to reduce the number of discharges and consequently the formingtime.

In aspects of the present disclosure, the adjusting means are a linear,hydraulic or pneumatic actuator.

In an aspect of the present disclosure, shown in FIG. 5, the device forstamping 10 comprises a blank-holder 60. The blank-holder is housed inthe open cavity 33. It is configured to exert a pressure between theblank 50 and the punch 21, when said blank is in position on the punch.The adjusting of this pressure will condition the feeding of the blankduring the forming thereof.

In an aspect of the present disclosure, the blank-holder is maintainedthrust against the second surface 52 of the blank 50 by means ofcompression 61.

In aspects of the present disclosure, the means of compression are aspring or a linear, hydraulic or pneumatic actuator, such as a cylinder,operating between the blank-holder and an inner surface 311 of thesecond frame 30.

An example of the method for stamping from such a device for stamping isnow described.

In a prior step, the blank 50 is cut, to the desired dimensions (lengthand width, or diameter, and thickness), in a sheet metal.

In a first step, referred to as step a), the blank 50 is positioned inthe device for stamping 10.

The blank 50, of substantially flat shape, is positioned between thefirst frame 20 and the second frame 30, as shown in FIG. 1.

In an aspect of the present disclosure, the blank 50 is arranged on theone hand on its central portion on the punch 21. The blank 50 isarranged in such a way that its first surface 51 bears against thebearing surface 211 of the punch.

When the device for stamping comprises a blank-holder 60, the blank 50is maintained bearing against the bearing surface 211 of the punch 21 bysaid blank-holder.

The blank 50 is arranged on the other hand, on its peripheral portion,between the means for generating a magnetic field 34 and the anvil 22.The first surface 51 of the blank is arranged facing the anvil 22, at adistance from the latter. The second face 52 of the blank is arrangedfacing the means for generating a magnetic field 34.

The blank bears against the bearing surface 211 of the punch 21. Theblank does not bear against the anvil 22.

In an aspect of the present disclosure, when the blank 50 has beenplaced on the punch, the punch 21 is moved, from its retracted position,in translation along the direction Z′Z, in order to offset the blank 50in such a way that the second surface 52 of said blank, on theperipheral portion of the blank, is placed in immediate proximity, forexample of about a millimetre, from the means for generating a magneticfield 34.

The method then comprises a second step, referred to as step b), ofdeforming the blank 50 via magnetic forming.

The ends of the blank 50, located in the vicinity of the means forgenerating a magnetic field 34, are subjected to a magnetic field comingfrom the means for generating a magnetic field 34 in such a way that apressure, axial, is exerted against the second surface 52 of the blank50, and tightly thrusts said blank against the anvil 22. The arrow shownin FIG. 2 shows the axial pressure exerted on the blank 50.

The blank 50 is consequently deformed to bear against the anvil 22.

During this step b) shown in FIG. 2, the means for generating a magneticfield 34 progressively deforms the peripheral portion of the blank 50 soas to obtained a first stamp with a depth P1, less than a depth P of thefinal stamp sought.

At the end of this step b), the blank 50 is deformed and has a firststamp.

In a third step, referred to as step c), the punch 21 is moved.

The punch 21 is translated by the movement means 23, in the directionZ′Z, in such a way as to drive in its movement the blank 50, by movingaway the peripheral portion of the blank 50 from the anvil 22, as shownin FIG. 3.

The movement of the punch 21, and consequently that of the blank 50, iscarried out in the direction opposite the direction of the movement ofthe blank 50 during the step b).

In an aspect of this third step, the punch 21 is moved in the directionZ′Z by a height that is sufficient for the second surface 52 of theblank 50 to return to the immediate vicinity of the means for generatinga magnetic field 34.

In an aspect of the present disclosure, the relative movement of thepunch 21 with respect to the means for generating a magnetic field 34and to the anvil 22 is carried out incrementally.

In an aspect of the present disclosure, the relative movement of thepunch with respect to the means for generating a magnetic field and tothe anvil is carried out continuously. The forming of the blank 50 bythe means for generating a magnetic field 34 can be considered asinstantaneous with respect to the movement of the punch. Indeed, theduration of the movement of the punch is generally very slow (of aboutone second) with respect to the duration of the magnetic pulse generatedby the means for generating a magnetic field 34 (of about onemicrosecond). In the particular case of this embodiment, the second andthird steps are carried out simultaneously without modifying the resultof said steps.

In a fourth step, the steps b) and c) are reproduced sequentially.

The steps b) and c) are reproduced until the obtaining of the depth P ofthe final stamped part that is sought to be obtained.

As the relative movement of the punch 21 takes place with respect to themeans for generating a magnetic field 34, said means for generating amagnetic field 34 advantageously exert an axial pressure on the blank 50in the direction of the anvil 22, thrusting said blank on said anvil.Said means for generating a magnetic field 34 also exert a radialpressure on the blank 50 in the direction of the punch 21, thrustingsaid blank on said punch. This radial pressure of the blank 50 againstthe punch 21 advantageously allows said blank to perfectly match theshape of the outer surface of the punch 21.

The number of iterations of the steps b) and c) depends in particular onthe material comprising the blank, on the desired depth of the stampedpart.

This present disclosure is not limited to the preferred embodimentsdescribed hereinabove as non-limiting examples and to the alternativesmentioned. It also relates to the alternative embodiments within thescope of those skilled in the art.

The description hereinabove clearly shows that through its variouscharacteristics and their advantages, this present disclosure achievesthe objectives that were set for it. In particular, it proposes a devicefor stamping suitable for the production of stamped parts, in particularof deep-drawn parts, without generating folds or tears on the part. Sucha device for stamping and of the associated method for stamping can makeit possible to work on the part mainly in compression but also inexpansion. In addition, as the high speeds tends to minimise theappearance of folds, the present disclosure advantageously makes itpossible to produce turned out edges.

What is claimed is:
 1. A Device for stamping a blank in order to producea stamped part comprising: a punch comprising a bearing surface, ananvil, means for generating a magnetic field, said device for stampingbeing configured, in an initial position, in such a way that: thebearing surface of the punch is intended for receiving a portion of afirst surface of the blank, the anvil and the means for generating amagnetic field are intended for being arranged on either side of anotherportion of the blank, with the anvil facing the first surface, and themeans for generating a magnetic field facing a second surface, oppositethe first surface, at a distance from said second surface, said meansfor generating a magnetic field being intended and configured to apply apressure on the blank towards the anvil, in a direction ZZ′, thrustingsaid blank on said anvil, the device for stamping comprising movementmeans arranged to move the punch, relative to the means for generating amagnetic field, in a direction opposite the direction ZZ′.
 2. The devicefor stamping according to claim 1, wherein the movement means comprise alinear actuator.
 3. The device for stamping according to claim 1,comprising adjusting means configured to adjust the space between theanvil and the means for generating a magnetic field.
 4. The device forstamping according to claim 1, comprising a blank-holder configured toimpose a retaining pressure on the movement of the blank, against thepunch.
 5. A method for stamping by magnetic pulse a blank in order toproduce a stamped part, using a device for stamping in accordance withclaim 1, comprising: a) positioning the blank in the device forstamping, b) subjecting the blank to a magnetic field caused by themeans for generating a magnetic field in such a way that a pressure isexerted on the second surface of the blank in a direction ZZ′ andthrusts said blank against the anvil, and c) moving the punch by themovement means in a direction opposite the direction ZZ′, with the stepsb) and c) being repeated until the desired shape is obtained for thefinished stamped part.
 6. The method for stamping according to claim 5,wherein as the punch moves, a radial pressure is exerted on the blank inthe direction of said punch, thrusting said blank on said punch.